At the moment when HDMI video output is stopped, we just clear the
enable bit and return. While it's unclear if this can cause any issues,
I think it's still better to wait for FRAMEDONE interrupt after clearing
the enable bit so that we're sure the HDMI IP has finished.

As we don't have any ready-made irq handling for HDMI, and this only
needs to be done when disabling the HDMI output, this patch implements a
simple loop with sleep, polling the FRAMEDONE bit.
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>